Many processes in the semiconductor industry require a reliable source of process gases for a wide variety of applications. Often these gases are stored in cylinders or vessels and then delivered to the process under controlled conditions from the cylinder. The semiconductor manufacturing industry, for example, uses a number of hazardous specialty gases such as phosphine, arsine, and boron-trifluoride for doping, etching, and thin-film deposition. These gases pose significant safety and environmental challenges due to their high toxicity and pyrophoricity (spontaneous flammability in air). In addition to the toxicity factor, many of these gases are compressed and liquefied for storage in cylinders under high pressure. Storage of toxic gases under high pressure in metal cylinders is often unacceptable because of the possibility of developing a leak or catastrophic rupture of the cylinder.
Low pressure storage and delivery systems have been developed which provide for adsorption of these gases onto a solid support. Storage and delivery systems of gases sorbed onib solid sorbents are not without their problems. They suffer from poor capacity and delivery limitations, poor thermal conductivity, and so forth.
The following patents and articles are illustrative of low pressure, low flow rate gas storage and delivery systems.
U.S. Pat. No. 4,744,221 discloses the adsorption of AsH3 onto a zeolite. When desired, at least a portion of the AsH3 is released from the delivery system by heating the zeolite to a temperature of not greater than about 175° C. Because a substantial amount of AsH3 in the container is bound to the zeolite, the effects of an unintended release due to rupture or failure are minimized relative to pressurized containers.
U.S. Pat. No. 5,518,528 discloses delivery systems based on physical sorbents for storing and delivering hydride, halide, and organometallic Group V gaseous compounds at sub-atmospheric pressures. Gas is desorbed by dispensing it to a process or apparatus operating at lower pressure.
U.S. Pat. No. 5,917,140 discloses a storage and delivery apparatus for dispensing a sorbable fluid from a solid-phase sorbent with enhanced heat transfer means incorporating radially extending arms each of which abuts and is secured in heat transfer relationship with the wall of the vessel.
WO/0211860 discloses a system for storage and delivery of a sorbate fluid in which the fluid is retained on a sorbent medium and desorption of the fluid from the medium is facilitated by inputting energy to the medium. Methods of energy input include thermal energy, photonic energy, particle bombardment, mechanical energy, and application of chemical potential differential to the sorbate fluid.
U.S. Pat. No. 6,101,816 discloses a fluid storage and dispensing system for a liquid whose vapor is to be dispensed. Associated with the system is a fluid flow port and fluid dispensing assembly associated with the port. The assembly comprises a fluid pressure regulator and a flow control valve. The arrangement is such that the gas from within the vessel flows through the regulator first prior to flow through the flow control element.